The present invention relates to an exposure control system of the type incorporating a device for driving a plurality of shutter blades, which also function as the diaphragm, in a rapid yet stable manner so as to attain the optimum exposure in response to the brightness of a subject.
There have been devised and demonstrated various types of the automatic exposure control systems, and they may be generally divided into two fundamental types. One type consists of a diaphragm or aperture setting mechanism including a moving coil, and a shutter mechanism, and depending upon the brightness of a subject, a suitable aperture is pre-selected and then the shutter is opened for a predetermined time. The other type consists of a plurality of shutter blades, which also function as the diaphragm, and a governer mechanism for driving the shutter blades to define a predetermined aperture depending upon the brightness of a subject and to be kept opened at this aperture for a predetermined time depending upon the brightness of the subject. In the former type, the response to the relatively quick variation in brightness of a subject is slow because of the moving coil. For instance, when the brightness of a subject is suddenly increased or reduced at the time when an aperture is set, over- or under-exposure results. Furthermore, the moving coil is easily susceptible to damages by shocks, and the overall construction of the automatic exposure control system is complex because it must incorporate not only the aperture setting mechanism but also the shutter mechanism. The latter type also has a defect that the governer is very complex in construction so that the exposure characteristics will change when it is used many times.